A fuel injector having an integrated spark plug is described in European Patent 0 661 446. The fuel injector with integrated spark plug is used for the direct injection of fuel into the combustion chamber of an internal combustion engine and for igniting the fuel injected into the combustion chamber. Due to the compact integration of a fuel injector with a spark plug, it is possible to save installation space at the cylinder head of the internal combustion engine. The conventional fuel injector with integrated spark plug has a valve body, which forms a sealing seat together with a valve-closure member that is actuated by means of a valve needle. Adjacent to this sealing seat is a spray-discharge orifice, which discharges at an end face of the valve body facing the combustion chamber. A ceramic insulation element insulates the valve body from a housing body against a high-voltage, the housing body being able to be screwed into the cylinder head of the internal combustion engine. Located on the housing body is a ground electrode so as to form an opposite potential to the valve body acted upon by high voltage. In response to a sufficient high voltage applied to the valve body, a spark arc-over occurs between the valve body and the ground electrode connected to the housing body.
A disadvantage of the conventional fuel injector with the integrated spark plug is that the position of the spark arc-over is undefined with respect to the fuel jet discharged from the spray-discharge orifice, since it is possible for the spark arc-over to occur at virtually any location in the lateral region of a valve-body projection. Thus, the conventional fuel injector does not allow a sufficiently precise and reliable ignition of the so-called jet root of the fuel jet spray-discharged from the spray-discharge orifice. However, a reliable and temporally precisely defined ignition of the fuel jet is required to achieve reduced emissions. Furthermore, the discharge orifice of the fuel jet may be subject to continually worsening carbon fouling or coking, which affects the form of the spray-discharged jet. Another disadvantage is that the ceramic extrusion coat of the fuel injector is relatively cost-intensive.
It is also disadvantageous that the operating voltage required to generate an ignition spark normally amounts to up to 25 kV, so that, on the one hand, the components required for the voltage generation or voltage transformation are cost-intensive and require more space, and on the other hand, the components are subjected to heavy loads by the high voltages and therefore have a short service life.